Triticones A and B, novel phytotoxins from the plant pathogenic fungus Drechslera tritici-repentis

Abstract

Table I. Secondary Tritium Isotope Effects in E2 Reactions of ArCLTCH2X and ArCL2CH2X (L = H or D) at 50 OC reaction kHlkT k d k T ( k~l k~L i c d ' 1" + EtONafEtOH 1.204 f 0.015 1.0314 f 0.010 1.106 f 0.033 2b + t-BuOKfr-BuOH 1.191 f 0.012 1.0274 f 0.008 1.092 f 0.026 a 2-Phenylethyltrimethylammonium bromide. 2-@-Chlorophenyl)ethyl tosylate. cFrom the relation k H / k T = (kD/kT)3,z6 (ref 8 and 9).transferred hydrogen are coupled with the stretching motion of the transferred hydrogen. The calculations also predict that the tunnel correction to the secondary tritium isotope effect should be diminished when the transferred atom is deuterium rather than protium. We report here experimental evidence that this is indeed the case.The experiments were modeled after the earlier ones by using 2-arylethyl derivatives tracer labeled with tritium in the j3-position. The resulting mixture can undergo the following elimination reactions 2 k r ArCL2CH2X + When L = H , k l / k 3 = (kH/kT)sec, and when L = D, k l / k 3 = manner previously describedZ for the reactions of 2-phenylethyltrimethylammonium ion (1) with ethoxide in ethanol and 2-(pchlorophenyl)ethyl tosylate (2) with tert-butoxide in tert-butyl alcohol, both at 50 OC. The results are given in Table I.The secondary kH/kT values are both substantial.' We pointed out earlier2 that the fractionation factors of Hartshorn and Shiner6,' predict k H / k T = 1.17 at 50 'c for complete rehybridmtion. Since proton transfer is incomplete in the transition state, it is unlikely that rehybridization would be complete, so the actual contribution of rehybridization to k H / k T is probably well below 1.17. The kD/kT are very much smaller than the kH/kT and remain smaller when converted to k H / k T (last column of Table I) by the r e l a t i~n s h i p~.~ (kD/kT)sec. We determined (kH/kT)= and (kD/kT)sec in theThis relationship is obeyed by the calculated semiclassical (without tunneling) primary (error I 3.8%) and secondary (error I 1.1%) isotope effects reported in ref 4. If masses are assumed to be in the ratio of reduced masses of C-H, C-D, and C-T instead of 1:2:3, the exponent in eq 1 becomes 3.34, but an exponent of ca. 6 is required to bring our calculated and directly measured kH/kT values into agreement. Any protium in the deuteriated substrate (<2% by NMR) would make kD/kT appear too large rather than too small. Table I are larger than predicted for rehybridization and larger than the ( k H / k T ) , values calculated from (kD/kT)sx is consistent only with model calculations that include t~n n e l i n g .~ The disagreements between columns 2 and 4 of Table I also constitute violations of the rule of the geometric mean.1° The principle behind the rule is that the isotope effect for a doubly labeled species should be very close to the product of the isotope effects for the corresponding singly labeled species. In other words, the two isotopes should exert their effects independently. This statement can be expressed alge-( 5 ) We believe our previously reported (ref 2) kH/kT f...

Metabolites of the fungus Arthropsistruncata

“…This conjugation would also account for the shielding of C 3 and the deshielding of C2 relative to the positions of the corresponding propenyl sp2 carbon signals in the spectrum of ( E ) -propeny lbenzene. Acetylation of cycloarthropsone (12) (12). These shifts are in accordance with those expected from a comparison of the spectra of phenol and phenyl acetate (7).…”

“…The I3c nlnr spectrum of arthropsolides B (25) Arthropsolide B (25) and C (26) are very similar in terms of structure and instability to the inseparable mixtures of spirostaphylotrichin G (27) and H (28) from Staphylotrichum coccosporum (lo), and triticone A (23) and B (24) from Staplzyloticlzum coccosporum (9) and Drechsleln tritici-repentis (12). Drechslera ti-itici-repentis is a major pathogen of wheat and it has been suggested that the retro-aldol intermediate 29 by which triticone A and B readily interconvert may be responsible for the lesions produced on wheat plants by this fungus (12).…”

“…Drechslera ti-itici-repentis is a major pathogen of wheat and it has been suggested that the retro-aldol intermediate 29 by which triticone A and B readily interconvert may be responsible for the lesions produced on wheat plants by this fungus (12). In an analogous fashion arthropsolide B (25) and C (26) may interconvert via the retroaldol intermediate 30 and these compounds may be responsible for inhibiting the growth of the blue-stain fungus Ophiostoma claviger~cm.…”

The identification and deletion of the polyketide synthase‐nonribosomal peptide synthase gene responsible for the production of the phytotoxic triticone A/B in the wheat fungal pathogen Pyrenophora tritici‐repentis

“…Three host specific toxins, the proteinaceous effectors ToxA and ToxB and the semi‐characterized small molecule effector ToxC have been described for Ptr (Effertz et al ., ; Ciuffetti et al ., ; Lamari and Strelkov, ). In addition, two classes of specialized metabolites, anthraquinones and triticones, have been reported as non‐specific phytotoxins (Sugawara et al ., ; Hallock et al ., ; Kachlicki and Wakulinski, ; Bouras and Strelkov, ). Anthraquinones are characterized by three fused aromatic rings and harbour a variety of substituents.…”

“…Triticones A to F were first purified from Ptr culture filtrates but have since been found, along with an additional 18 other triticone compounds, in 5 other ascomycete fungi, Staphylotrichum coccosporum , Curvularia pallescens , Pyrenophora seminiperda , Cochliobolus lunatus and Bipolaris spp. (Sugawara et al ., ; Sandmeier and Tamm, ,b, ; Hallock et al ., ; Abraham et al ., ; de Almeida et al ., ; Wang et al ., ). Triticone A and B are known to be phytotoxic, producing yellowish‐brown lesions following leaf puncture assays on a range of hosts including wheat.…”